1. Field of the Invention
The present invention relates generally to an apparatus and method for implementing an all-optical OR logic gate using the gain saturation characteristic of a single semiconductor optical amplifier and, more particularly, to technology for implementing a new all-optical OR logic gate that performs an all-optical logic operation using an optical signal, which is transferred from a certain point of an optical circuit, such as an optical computing circuit, as a pump signal and a probe signal.
2. Description of the Related Art
In accordance with a recent trend, the demand for a high-speed and large-capacity system is rapidly increasing. Meanwhile, the information processing capacity of a backbone network will increase from several hundreds of Gbit/s to several Tbit/s because the purpose of a future information/communication network is to provide multimedia services, including voice signals, still images and moving images. Accordingly, in order to transmit, process and exchange a large volume of data at high speed, all-optical signal processing technology is becoming core technology. In particular, all-optical logic operation that is capable of avoiding cumbersome electro-optic conversion is core technology for an all-optical signal processing system. Accordingly, the development of an all-optical logic gate that is important in next generation optical computing and all-optical signal processing fields is actively being carried out.
Up to now, an all-optical logic gate for ultrafast optical information processing has mainly used the nonlinear characteristic of a Semiconductor Optical Amplifier (SOA). In particular, all-optical logic gates were implemented through an Ultrafast Nonlinear Interferometer (UNI) [N. S. Patel, K. L. Hall and K. A. Rauschenbach, Opt. Lett., Vol. 21, 1466 (1996)] that uses the nonlinear characteristic and variation in refractive index of an SOA, a Michelson interferometer [T. Fjelde, D. Wolfson, A. Kloch, C. Janz, A. Coquelin, I. Guillemot, F. Gabortit, F. Poingt, B. Dagens, and M. Renauo, Electron. Lett., Vol. 36, 813 (2000)] in which SOAs are integrated, and through two SOAs with Cross Gain Modulation (XGM) [Korean Pat. No. 0452617 entitled “Apparatus for implementing all-optical OR logic gate using semiconductor optical amplifier,” issued to Byun Young-Tea, Jun Young-Min, Kim Jae-Hun, Lee seok, Woo duck-Hwa, Kim Sun-Ho and Kang Kwang-Nam on Oct. 4, 2004] (hereinafter referred to as “Cited document 1”) that uses the gain saturation and wavelength conversion characteristics of two SOAs.
In the above-described all-optical OR logic gate using SOAs with XGM, a probe signal and a pump signal pass through two SOAs. In this case, the width of a pulse signal increases because a gain recovery time is slower than a gain saturation time, so that operating speed is limited to below 2.5 Gbit/s. Furthermore, the logic gate uses two SOAs and, therefore, the structure of the logic gate is very complicated. Accordingly, to solve the two above-described disadvantages, the present invention implements an all-optical OR logic gate which has not only an operating speed above 2.5 Gbit/s but also a simplified structure using the gain saturation characteristic of a single SOA.
Furthermore, the present invention can operate at above 10 Gbit/s using SOAs with XGM, which has an operational principle identical to that of an all-optical AND logic gate [Korean Pat. Appl. No. 10-2003-64638 entitled “All-optical AND gate using gain saturation of SOA,” filed by Kim Jae-Hun, Kim Byoung-Chae, Byun Young-Tea, Jun Young-Min, Lee seok, Woo duck-Hwa, Kim Sun-Ho and Lee Jong-Chang on Sep. 18, 2003], an all-optical NAND logic gate [Korean Pat. Appl. No. 10-2001-58131 entitled “Technology for implementing all-optical NAND logic gate using SOA,” filed by Kim Jae-Hun, Byun Young-Tea, Jun Young-Min, Lee seok, Woo duck-Hwa, Kim Sun-Ho and Kang Kwang-Nam on Sep. 20, 2001], an all-optical NOR logic gate [Korean Pat. Appl. No. 10-2003-25361 entitled “Apparatus and method for implementing all-optical NOR logic gate using gain saturation of SOA,” filed by Byun Young-Tea, Kim Jae-Hyun, Jun Young-Min, Lee seok, Woo duck-Hwa, Kim Sun-Ho and Lee Jong-Chang on Apr. 22, 2003] (hereinafter referred to as “Cited document 2”), and an all-optical XOR logic gate [Korean Pat. No. 0418654 entitled “Method of implementing all-optical XOR logic gate using semiconductor optical amplifier”, issued to Kim Jae-Hun, Byun Young-Tea, Jun Young-Min, Lee seok, Woo duck-Hwa, Kim Sun-Ho and Kang Kwang-Nam on Feb. 2, 2004]. Accordingly, the present invention may be applicable to the implementation of complicated all-optical circuits for optical computing or all-optical signal processing systems.